Cyclic olefin polymers have high glass transition temperatures and high stiffness, however, they suffer from very poor impact properties and are too brittle for many applications. Numerous attempts have been made to improve their impact properties by blending with modifiers of many types, and their stiffness by blending with reinforcements. None of these previous attempts has been very successful, and for the most part, cyclic olefin polymers have been relegated to applications taking advantage of only their optical clarity, moisture resistance, and good birefringence properties.
Polyolefins, and in particular those of the polyethylene and polypropylene groups, are low-cost, lower-density thermoplastics which melt readily and are resistant to chemicals. These materials therefore have many uses in areas such as general household items and electrical and electronic parts. However, polyolefins usually have poor mechanical properties and relatively low heat distortion temperatures (HDT). For example, a typical polypropylene homopolymer has a flexural modulus of about 1.9 GPa, a heat distortion temperature at 0.46 MPa of about 126° C., and a notched Izod impact resistance of about 48 J/m. These plastics are therefore unsuitable for use in areas which require high heat resistance, high mechanical strength, and/or high impact resistance.
To improve their impact resistance, polypropylene homopolymers are often blended with ethylene-propylene rubber (EPR) or ethylene-propylene-diene (EPDM) rubber. EPR and EPDM rubbers are ideal for impact modification, because they remain ductile until their glass transition temperatures at about −45° C. and effectively toughen polypropylene even at −29° C., a common testing temperature. EPR, EPDM, and polypropylene have similar polarities, so small rubber domains can be well dispersed in the polypropylene. Impact resistance can also be improved by polymerizing the propylene with a few percent of ethylene to make impact polymers. However, these improved impact properties come with decreased modulus and lowered heat distortion temperatures. Thus, a typical polypropylene impact polymer containing EPR has flexural modulus of about 1.0 GPa, a heat distortion temperature at 0.46 MPa of about 92° C., a room temperature notched Izod impact strength so high that no test samples break (approx. 500 J/m or more), and generally has only ductile failures in the instrumented impact test at −29° C. (approx. 43 J of energy adsorbed).
To achieve more balanced properties, polypropylenes can be blended with both ethylene-propylene or ethylene-propylene-diene elastomers and inorganic fillers such as talc, mica, or glass fibers. Talc and mica reinforcements are generally preferred to glass fibers, because the compounded polymers have better surface and flow properties. An example of these materials is ExxonMobil's AS65 KW-1ATM, which has a flexural modulus of about 2.4 GPa, a heat distortion temperature at 0.46 MPa of about 124° C. and a notched Izod Impact of about 400 J/m. These polymer blends have a good balance of properties and are used in automotive interior applications. However, these blends can not be used for some automotive structural applications, where useful materials need heat distortion temperatures at 0.46 MPa of at least 140° C. and at 1.80 MPa of at least 120° C., together with a modulus of at least 2.5 GPa and a room temperature notched Izod impact of at least 100 J/m.
In an attempt to achieve balanced properties that exceed those of blended polypropylenes, blends of cyclic olefin polymers with polyolefins have also been proposed. For example, polymers of ethylene with norbornene and with 2,3-dihydrodicyclopentadiene are disclosed in U.S. Pat. No. 2,799,668 (Jul. 16, 1957) and U.S. Pat. No. 2,883,372 (Apr. 21, 1959). However, these polymers use TiCl4 as the catalyst and are polymerized by ring opening metathesis—the cyclic olefin rings opened during polymerization with ethylene, leaving a residual double bond in the backbone of the polymer. Because the rings open, the chains are less rigid than addition polymerization cyclic olefin polymers. The residual unsaturation in their backbones also make these polymers oxidatively unstable at high temperatures. Consequently, although these polymers have desirable rigidity and transparency, they are poor in heat resistance.
U.S. Pat. No. 3,494,897 discloses a high pressure, peroxide initiated, radical polymerization to make ethylene/cyclic olefin polymers but these polymerizations can only incorporate small amounts of the cyclic olefins. As a result, the polymers do not have high glass transition temperatures.
Several blends of ethylene/norbornene polymers with polyolefins were described by researchers at VEB Leuna-Werke in the early 1980s (DE 2731445 C3, DD 150751, DD 203061, DD 203059, DD 203062, DD 205916, DD 206783, DD 209840, DD 214851, DD 214849, and DD 214850). However, these blends were made before the discovery of either the Ziegler-Natta vanadium/aluminum or metallocene addition polymerization catalysts. The ethylene/norbornene polymers used in these blends were made with catalysts that open cyclic rings during polymerization and lead to residual unsaturation in the polymer backbones. The Vicat softening temperatures exemplified in these patents range from 114 to 133° C. indicating that these polymers do not have the heat stability required for automotive structural applications. In this respect, it is to be appreciated that Vicat softening temperatures are generally about 10° C. higher than the glass transition temperature of a glassy polymer, whereas the glass transition temperature of a glassy polymer is generally about 10° C. higher than its heat distortion temperature at 0.46 MPa. Thus Vicat softening temperatures from 114 to 133° C. are roughly equivalent to heat distortion temperatures of about 94 to 113° C. using the 0.46 MPa load.
U.S. Pat. No. 4,614,778 discloses a random polymer of ethylene with a 1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene and optionally an alpha-olefin having at least three carbon atoms or a cycloolefin, such as norbornene. The mole ratio of polymerized units from the 1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene to polymerized units from ethylene is from 3:97 to 95:5 and the 1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene is incorporated in the ethylene polymer chain using a Ziegler-Natty vanadium/aluminum catalyst. The cyclic olefin rings do not open during polymerization, and the resultant polymers contain no residual unsaturation in their backbone. Thus, these polymers have high heat distortion temperatures and glass transition temperatures as high as 171° C. However, the polymers are quite brittle, when pressed into films, and all are polymers of ethylene and cyclic olefin comonomers containing at least four fused rings. The disadvantage of these larger comonomers is that extra Diels-Alder addition reactions are required to build them up from ethylene and cyclopentadiene, making them more expensive to synthesize than norbornene or dicyclopentadiene. No blends are exemplified in this patent.
U.S. Pat. No. 5,087,677 describes the polymerization of ethylene and cyclic olefins, particularly norbornene, using zirconium and hafnium metallocene catalysts. Like the vanadium/aluminum polymerized polymers described in U.S. Pat. No. 4,614,778, the metallocene polymerized polymers do not have residual unsaturation in their backbones and the cyclic olefins do not ring open. Consequently, these metallocene ethylene/cyclic olefin polymers have high heat stabilities and glass transition temperatures, with values as high as 163° C. for the glass transition temperature being exemplified. There is brief mention, but no exemplification, of alloying the polymers with other polymers, such as polyethylene, polypropylene, (ethylene/propylene)polymers, polybutylene, poly-(4-methyl-1-pentene), polyisoprene, polyisobutylene, and natural rubber.
U.S. Pat. No. 4,918,133 discloses a cycloolefin type random polymer composition, which is alleged to exhibit excellent heat resistance, chemical resistance, rigidity, and impact resistance, and which comprises (A) a random polymer containing an ethylene component and a cycloolefin component and having an intrinsic viscosity [η] of 0.05-10 dl/g as measured at 135° C. in decalin and a softening temperature (TMA) of not lower than 70° C., and (B) one or more non-rigid polymers selected from the group consisting of: (i) a random polymer containing an ethylene component, at least one other α-olefin component and a cycloolefin component and having an intrinsic viscosity [η] of 0.01-10 dl/g as measured at 135° C. in decalin and a softening temperature (TMA) of below 70° C., (ii) a non-crystalline to low crystalline α-olefin type elastomeric polymer formed from at least two α-olefins, (iii) an α-olefin-diene type elastomeric polymer formed from at least two α-olefins and at least one non-conjugated diene, and (iv) an aromatic vinyl type hydrocarbon-conjugated diene polymer or a hydrogenated product thereof, and optionally (c) an inorganic filler or organic filler. The cycloolefin component of the polymer (A) can be a large number of 1 to 4-ring bridged cyclic olefins and, although these include norbornene, the only material exemplified is 1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene (DMON) and a methyl-substituted version thereof.
U.S. Pat. No. 6,255,396 discloses a polymer blend useful for fabrication into transparent articles for medical applications and comprising 1-99% by weight of a first component obtained by polymerizing a norbornene monomer and an ethylene monomer, and 99% to 1% by weight of a second component comprising an ethylene polymer with an α-olefin having 6 carbon atoms. The first component has a glass transition temperature of from 50° C. to 180° C., but the second blend component has a softening points above 30° C. due to either its melting point (softening temperatures are slightly below the melting point) or its glass transition temperatures (softening point is typically about 10° C. above Tg). No measurements of flexural modulus or impact strengths are reported in the patent and no inorganic fillers are exemplified.
U.S. Pat. No. 6,590,033 discloses a polymer blend similar to that described in U.S. Pat. No. 6,255,396 but with the second component comprising a homopolymer or polymer of a diene having from 4 to 12 carbons. Such diene polymers typically have softening points above 30° C. or solubility parameters that are too different from those of the cyclic olefin polymers to be compatible. For example, the Bicerano solubility parameter for poly(1,4-butadiene) is 17.7 J0.5/cm1.5 compared with 16.88 J0.5/cm1.5 for the cyclic olefin polymers. (Values are from Table 5.2 in Prediction of Polymer Properties, 3rd edition by Jozef Bicerano published by Marcel Dekker in 2002.) In addition, poly(1,4-butadiene) is too polar to be effective at toughening cyclic olefin polymers.
U.S. Pat. No. 6,844,059 discloses long-fiber-reinforced polyolefin structure of length≧3 mm, which comprises a) from 0.1 to 90% by weight of at least one polyolefin other than b), b) from 0.1 to 50% by weight of at least one amorphous cycloolefin polymer, such as an ethylene/norbornenes polymer, c) from 5.0 to 75% by weight of at least one reinforcing fiber, and d) up to 10.0% by weight of other additives. The polyolefin a) may be obtained by addition polymerization of ethylene or of an α-olefin, such as propylene, using a suitable catalyst and generally is a semi-crystalline homopolymer of an α-olefin and/or ethylene, or a polymer of these with one another.
In Die Angewandte Makromolekulare Chemie 256 (1998), pp. 101-104, Stricker and Mulhaupt describe blends of an ethylene/norbornene polymer containing only 40 wt. % norbornene. The thermal stability of this polymer is not reported, however the glass transition temperature can be estimated at less than 60° C. The rubber used to toughen the cyclic olefin polymer is a polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) polymer. Polystyrene blocks in this polymer have glass transition temperatures in the range 83-100° C., giving this modifier a softening temperature of more than 80° C.
In an article entitled “Rubber Toughened and Optically Transparent Blends of Cyclic Olefin Polymers” in Polymer Engineering and Science, Vol. 40(12), p. 2590-2601, December, 2000, Khanarian describes unfilled blends of the ethylene/norbornene polymer TOPAS 6013 with thermoplastic elastomers such as styrene-butadiene-styrene (SBS), styrene-ethylene-butadiene-styrene (SEBS), and styrene-ethylene-propylene-styrene (SEPS). The TOPAS 6013 has a glass transition temperature of 140° C. and it is reported that blending with less than 5 wt % of the elastomer allows the impact strength to be increased to greater than 50 J/m (Notched Izod) while keeping the optical haze below 5%. Using high loadings of the styrenic block polymers, Khanarian achieves a notched Izod impact strength as high as 520 J/m with 30 wt. % polystyrene-b-polybutadiene-b-polystyrene. This modifier has a softening point above 30° C. due to the glass transition temperature of the polystyrene blocks. Khanarian also exemplifies some blends with ethylene-propylene-diene terpolymers, but the impact strength reported is only 188 J/m with a 20 wt. % loading. Measured heat distortion temperatures are not presented in this paper but, given the low glass transition temperature of the TOPAS 6013, are probably less than 125° C. at 0.46 MPa.
Other references of interest include U.S. Pat. Nos. 4,874,808; 4,992,511; 5,428,098; 5,359,001; 5,574,100; 5,753,755; 5,854,349; 5,863,986; 6,090,888; 6,225,407; US 2003/0125464 A1; U.S. Pat. Nos. 6,596,810 B1; 6,696,524 B2; 6,767,966 B2; US 2004/0236024 A1; and US 2005/0014898 A1.
According to the invention, it has now been found that blending high glass transition temperature cyclic olefin polymers with compatible, low glass transition temperature polyolefin elastomers, and fillers can produce polymer blends having a desirable combination of high stiffness, impact toughness, and thermal stability making certain of the blends suitable for use in automotive structural applications.